Process for the preparation of 2,3,3,3-tetrafluoropropene

ABSTRACT

The present invention provides a process for preparing 2,3,3,3-tetrafluoropropene from 1,1,1,2,3-pentachloropropane and/or 1,1,2,2,3-pentachloropropane, comprising the following steps: (a) catalytic reaction of 1,1,1,2,3-pentachloropropane and/or 1,1,2,2,3-pentachloropropane with HF into a reaction mixture comprising HCl, 2-chloro-3,3,3-trifluoropropene, 2,3,3,3-tetrafluoropropene, unreacted HF, and optionally 1,1,1,2,2-pentafluoropropane; (b) separating the reaction mixture into a first stream comprising HCl and 2,3,3,3-tetrafluoropropene and a second stream comprising HF, 2-chloro-3,3,3-trifluoropropene and optionally 1,1,1,2,2-pentafluoropropane; (c) catalytic reaction of the second stream into a reaction mixture comprising 2,3,3,3-tetrafluoropropene, HCl, unreacted 2-chloro-3,3,3-trifluoropropene, unreacted HF and optionally 1,1,1,2,2-pentafluoropropane and (d) feeding the reaction mixture of step (c) directly without separation to step (a).

FIELD OF THE INVENTION

The present invention relates to the preparation of2,3,3,3-tetrafluoropropene (HFO-1234yf). More particularly, the presentinvention relates to a two reaction step process whereinpentachloropropane, including 1,1,1,2,3-pentachloropropane (HCC-240db)and/or 1,1,2,2,3-pentachloropropane (HCC-240aa), is first contacted withhydrogen fluoride (HF), this first step (a) providing2-chloro-3,3,3-trifluoropropene (HCFO-1233xf), which after separation isthen converted into HFO-1234yf in a second reaction step (c).

The desired product, HFO-1234yf is known to have utility as a foamblowing agent, refrigerant, aerosol propellant, heat transfer media,fire extinguisher, etc. Furthermore, HFO-1234yf is known to have zeroOzone Depletion Potential (ODP) and very low Global Warming Potential(GWP) of much less than 150.

TECHNICAL BACKGROUND

The protocol of Montreal for the protection of the ozone layer led tothe end of the use of chlorofluorocarbons (CFCs). Less aggressivecompounds for the ozone layer, such as the hydrofluorocarbons (HFCs)e.g. HFC-134a replaced chlorofluorocarbons. These latter compounds wereindeed shown to provide greenhouse gases. There exists a need for thedevelopment of technologies, which present a low ODP (ozone depletionpotential) and a low GWP (global warming potential). Although thehydrofluorocarbons (HFCs), which are compounds which do not affect theozone layer, were identified as interesting candidates, they exhibit arelatively high GWP value. There still exists the need to find compoundswhich exhibit a low GWP value. Hydrofluoroolefins (HFO) were identifiedas being possible alternatives with very low ODP and GWP values.

Several processes of production HFOs compounds, in particular ofpropenes, were developed. US2009/0240090 discloses the gas-phasereaction of 1,1,1,2,3-pentachloropropane (HCC-240db) into product2-chloro-3,3,3-trifluoropropene (HCFO-1233xf). Example 3 uses a catalystcomprised of fluorinated Cr₂O3. The product HCFO-1233xf thus produced isthen converted into product 2-chloro-1,1,1,2-tetrafluoropropane(HCFC-244bb) in a liquid phase reaction. This product HCFC-244bb is thenconverted into the desired HFO-1234yf. This process comprises threereaction steps.

WO2005/108334, example 3, discloses that HCC-240db is passed through aflow reactor for a contact time for about 5 to 50 seconds at about250-400° C. in the presence of 5 molar excess of HF over a 50 g ⅛-inchCr₂O₃ catalyst bed to give HCFC-244db(2-chloro-1,1,1,3-tetrafluoropropane). It is further indicated that theHCFC-244db is then dehydrochlorinated by passing it over a Cr₂O₃catalyst (50 g) at 425-550° C. with a contact time of 25 to 30 secondsto afford product HFO-1234ze (1,3,3,3-tetrafluoropropene).

The literature is generally about a scheme involving preparation ofHFO-1234yf via the HCFC-244 route.

There is still a need for further processes for manufacturingHFO-1234yf.

SUMMARY OF THE INVENTION

The invention is based on the finding that it is possible to prepare thecompound HFO-1234yf starting from pentachloropropane. The processaccording to the present invention includes two reaction steps with aseparation step in between.

The present invention is advantageous over processes described in priorart in that the process includes the ability to maximize raw materialutilization and product yields for a long time. It is also characterisedby the ability to handle and recover by-products that are commerciallyvaluable. Moreover, the process is conducted without preparing in anintermediate stage the product HCFC-244bb(2-chloro-1,1,1,2-tetrafluoropropane).

Hence, the invention provides a process for preparing2,3,3,3-tetrafluoropropene from 1,1,1,2,3-pentachloropropane and/or1,1,2,2,3-pentachloropropane, comprising the following steps:

(a) catalytic reaction of 1,1,1,2,3-pentachloropropane and/or1,1,2,2,3-pentachloropropane with HF into a reaction mixture comprisingHCl, 2-chloro-3,3,3-trifluoropropene, 2,3,3,3-tetrafluoropropene,unreacted HF, and optionally 1,1,1,2,2-pentafluoropropane;

(b) separating the reaction mixture into a first stream comprising HC1and 2,3,3,3-tetrafluoropropene and a second stream comprising HF,2-chloro-3,3,3-trifluoropropene and optionally1,1,1,2,2-pentafluoropropane;

(c) catalytic reaction of the second stream into a reaction mixturecomprising 2,3,3,3-tetrafluoropropene, HCl, unreacted2-chloro-3,3,3-trifluoropropene, unreacted HF and optionally1,1,1,2,2-pentafluoropropane and

(d) feeding the reaction mixture of step (c) directly to step (a)without separation.

The term “Organics” is defined herein as any compound comprising carbonatom, hydrogen atom and chlorine atom and/or fluorine atom such as1,1,1,2,3-pentachloropropane, 1,1,2,2,3-pentachloropropane,1,1,1,2,2-pentafluoropropane and 2-chloro-3,3,3-trifluoropropene.

Embodiments are the following:

-   -   step (a) and/or step (c) is carried out in a gas-phase.    -   the process is carried out in presence of oxygen or chlorine.    -   The molar ratio of oxygen with respect to Organics in step (a)        is 0.005 to 2, preferably 0.01 to 1.5.    -   The molar ratio of oxygen with respect to Organics in step (c)        is 0.005 to 2, preferably 0.01 to 1.5.    -   step (a) and/or step (c) is carried out in a gas-phase in the        presence of a chromium based catalyst.    -   the 1,1,1,2,3-pentachloropropane contains up to 40 mol % of        isomer 1,1,2,2,3-pentachloropropane.    -   the process is continuous.    -   Step (a) and/or step (c) is carried out at a pressure from 0.1        to 50 bar absolute, preferably from 0.3 to 15 bar absolute.    -   Step (a) and/or step (c) is carried out at a temperature of from        100 to 500° C., preferably from 200 to 450° C.    -   Step (a) and/or step (c) is or are carried out at a molar ratio        HF:Organics from 4:1 to 100:1, preferably 5:1 to 50:1.    -   Contact time in step (a) is between 1 and 50 s, preferably        between 2 and 40 s.    -   Contact time in step (c) is between 1 and 100 s and preferably        between 5 and 50 s.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic representation of a process.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention relates to a process for manufacturing2,3,3,3-tetrafluoropropene from 1,1,1,2,3-pentachloropropane and/or1,1,2,2,3-pentachloropropane. The process generally comprises twoseparate reaction steps. In the first step (a), a raw materialcomprising 1,1,1,2,3-pentachloropropane and/or1,1,2,2,3-pentachloropropane reacts, in the presence of a catalyst, withan excess of anhydrous HF, preferably in a vapor phase, to produce amixture of HCl, 2-chloro-3,3,3-trifluoropropene,2,3,3,3-tetrafluoropropene. The first reaction step can be performed ina single reactor. The effluent stream exiting the reactor may optionallycomprise additional components such as 1,1,1,2,2-pentafluoropropane(HFC-245cb) and unreacted HF.

The product stream of the first step (a) is then sent to a separationstep (b), preferably distillation, to give a first stream comprising HCland HFO-1234yf and a second stream comprising HF,2-chloro-3,3,3-trifluoropropene and optionally1,1,1,2,2-pentafluoropropane. The second stream is then fed in a secondreactor optionally with fresh HF in conditions sufficient to give aproduct stream comprising HFO-1234yf, HFC-245cb, together with unreactedHCFO-1233xf and HF. This product stream is sent directly to step (a).

Step (a)

Step (a) of the present process involves contacting fresh HCC-240dband/or HCC-240aa and the reaction products from step (c) with HF in thereaction zone in the presence of a catalyst, preferably in the gasphase, under conditions sufficient to give fluorination productscomprising mainly HCFO-1233xf and HFO-1234yf.

Typically, the step (a) is carried out with a molar ratio HF:Organicsfrom 4:1 to 100:1, preferably 5:1 to 50:1.

Typically, the process of the invention is carried out at a pressurefrom 0.1 to 50 bar absolute, preferably 0.3 to 15 bar absolute.

Typically, the process of the invention is carried out at a temperatureof from 100 to 500° C., preferably from 200 to 450° C.

Contact times (catalyst volume divided by the total flow rate ofreactants and co-feeds, adjusted to the operating pressure andtemperature) are typically from 1 to 50 sec, preferably from 2 to 40sec.

-   -   An oxygen co-feed may be used to extend the catalyst lifetime,        typically the molar ratio of oxygen/Organics is from 0.005 to 2,        preferably 0.01 to 1.5.

The oxygen can be introduced as an oxygen-containing gas such as air,pure oxygen, or an oxygen/nitrogen mixture.

A chlorine cofeed may also be used instead of the oxygen cofeed (withthe same operating conditions).

Chlorine can be introduced as a chlorine-containing gas such as purechlorine, or a chlorine/nitrogen mixture.

Catalyst

The catalyst is for example a catalyst based on a metal including atransition metal oxide or a derivative or halide or oxyhalide such ametal. Catalysts are e.g. FeCl₃, chromium oxyfluoride, chromium oxides(that can optionally be subject to fluorination treatments), chromiumfluorides, and mixtures thereof. Other possible catalysts are thecatalysts supported on carbon, catalysts based on antimony, catalystsbased on aluminum (as AlF₃ and Al₂O₃ and oxyfluoride of alumina andaluminum fluoride). Generally speaking, catalysts that can be used arechromium oxyfluoride, aluminium fluoride and oxyfluoride, and supportedor unsupported catalyst containing a metal such as Cr, Ni, Fe, Zn, Ti,V, Zr, Mo, Ge, Sn, Pb, Mg, Sb. Reference can also be made to thedisclosures of WO-A-2007/079431, at page 7, lines 1-5 and 28-32,EP-A-939071, at paragraph [0022], WO2008/054781 at page 9 line 22 topage 10 line 34, WO2008/040969 in claim 1, all incorporated herein byreference.

Prior to its use, the catalyst is subjected to activation with air,oxygen or chlorine and/or with HF.

Prior to its use, the catalyst is preferably subjected to an activationprocess with oxygen or air and HF at a temperature of 100-500° C.,preferably from 250-500° C. and more preferably from 300-400° C. Theperiod of activation is preferably from 1 to 200 h and more preferablyform 1 to 50 h.

This activation can be followed by a final fluorination activation stepin the presence of an oxidizing agent, HF and Organics. The molar ratioof HF/Organics is preferably from 2 to 40 and the molar ratio ofoxidizing agent/Organics is preferably from 0.04 to 25. The temperatureof final activation is preferably from 300 to 400° C. and morepreferably for about 6 to 100 h.

The catalyst is preferably a chromium based catalyst and more preferablya mixed catalyst comprising chromium.

A preferred embodiment uses a particular catalyst, which is a mixedcatalyst, containing both chromium and nickel. The molar ratio Cr:Ni,with respect to the metallic element is generally between 0.5 and 5, forexample between 0.7 and 2, including close to 1. The catalyst maycontain in weight from 0.5 to 20% chromium and 0.5 to 20% nickel,preferably between 2 and 10% of each metal.

The metal may be present in metallic form or as derivatives, includingoxide, halide or oxyhalide. These derivatives, including halide andhalide oxides, are obtained by activation of the catalytic metal.Although the activation of the metal is not necessary, it is preferred.

The support is preferably made from aluminum. There are several possiblecarriers such as alumina, activated alumina or aluminum derivatives.These derivatives include aluminum halides and halide oxides ofaluminum, for example described in U.S. Pat. No. 4,902,838, or obtainedby the activation process described below.

The catalyst may include chromium and nickel in a non-activated oractivated form, on a support that has been subjected to activation ornot.

Reference can be made to WO2009/118628, and especially to the disclosureof the catalyst from page 4, line 30 to page 7, line 16, which isincorporated herein by reference.

Another preferred embodiment uses a mixed catalyst containing chromiumand at least an element chosen from Mg and Zn. The atomic ratio of Mg orZn/Cr is preferably from 0.01 and 5.

Step (b)

The product stream of step(a) comprising HCl,2-chloro-3,3,3-trifluoropropene, 2,3,3,3-tetrafluoropropene, unreactedHF, and optionally 1,1,1,2,2-pentafluoropropane enters a separationunit, for example a distillation column, to give a first streamcomprising HCl and 2,3,3,3-tetrafluoropropene and a second streamcomprising HF, 2-chloro-3,3,3-trifluoropropene and optionally1,1,1,2,2-pentafluoropropane. Step (b) can be performed at a temperaturepreferably from −90 to 150° C. and more preferably from −85 to 100° C.,and at a pressure preferably from 0.1 to 50 bar abs and more preferablyfrom 0.3 to 5 bar abs.

The first stream leaves the reaction system and enters an acidproduction unit to produce hydrochloric acid and HFO-1234yf.

HFO-1234yf and intermediate products are readily recovered by any meansknown in the art, such as by scrubbing, washing, extraction, decantationand preferably distillation. Any stream can also be further purified bydistillation techniques.

Step (c)

Step (c) of the present invention is a fluorination reaction, preferablygas phase, of the second stream of step (b) with HF in the presence of acatalyst and it comprises mainly fluorination of2-chloro-3,3,3-trifluoro-1-propene obtained in step (a) in2,3,3,3-tetrafluoro-1-propene, the desired product.

Step (c) can be carried out in a single or multiple gas-phase reactor.

This step of the process of the present invention, as well as the entireprocess, is preferably run continuously.

This step involves mainly contacting HCFO-1233xf with HF in the reactionzone in a gas phase, under conditions sufficient to convert theHCFO-1233xf to fluorination products comprising HFO-1234yf andHFC-245cb. Such conditions are given below. In addition to thefluorinated products, unreacted HCFO-1233xf, unreacted HF and otherco-produced underfluorinated intermediates which may be present in minoramounts are sent directly to step (a).

Typically, this step is carried out with a molar ratio HF:Organics from4:1 to 100:1, more preferably 5:1 to 50:1.

Typically, this step is carried out at a pressure from 0.1 to 50 bars,preferably 0.3 to 15 bars absolute.

Typically, this step is carried out at a temperature of from 100 to 500°C., preferably from 200 to 450° C.

Contact times (catalyst volume divided by the total flow rate ofreactants and co-feeds, adjusted to the operating pressure andtemperature) are typically from 1 to 100 sec, preferably from 5 to 50sec.

An oxygen co-feed may be used to extend the catalyst lifetime, typicallythe molar ratio of oxygen/Organics is from 0.005 to 2, preferably 0.01to 1.5.

The oxygen can be introduced as an oxygen-containing gas such as air,pure oxygen, or an oxygen/nitrogen mixture.

A chlorine cofeed may also be used in lieu of the oxygen cofeed (withthe same operating conditions).

Chlorine can be introduced as a chlorine-containing gas such as purechlorine, or a chlorine/nitrogen mixture.

The catalyst described above can be used in this step. It can be similarto the one used in step (a) or different.

Reaction steps (a) and (c) are implemented in a dedicated reactor forreactions involving halogens. Such reactors are known to those skilledin the art and can include linings based eg Hastelloy®, Inconel®, Monel®or fluoropolymers. The reactor may also include means of heat exchange,if necessary.

Besides advantages described above, the reaction step © which is acritical step can be performed in the absence of the huge amount of HClgenerated in the first step and also in some embodiment such as when thereactor of step (c) is placed above that of the reactor of step (a),loading and unloading of the catalyst is easier. Moreover, sinceunreacted HCFO-1233xf coming from step (c) also reacts in step(a), theyield of HFO-1234yf based on pentachloropropane is higher.

The present invention can be practised in a compact plant since only oneseparation cycle is needed and is also low energy consuming.

FIG. 1 represents the process carried out in one embodiment of theinvention. The first gas-phase reactor (3) is fed with fresh HCC-240db(2) and optionally fresh HF (1). The reaction mixture (4) exiting thereactor comprises HCl, HCFO-1233xf, unreacted HF, HFO-1234yf andoptionally HFC-245cb. This reaction stream is separated by distillation(5) into a first stream (6) comprising HCl, HFO-1234yf optionally withsmall amount of HF and minor amounts of HFC-245cb and HFO-1233xf. Asecond, heavier, stream (7) is obtained at the bottom of thedistillation column, and comprises HF, HCFO-1233xf, HFC-245cb.HFO-1234yf can be separated and purified from stream (6) usingappropriate known methods.

The second reactor (11) is fed by stream (10) which is consists of thesecond stream (7), optionally with fresh HF (8)and oxygen (9). Thereaction mixture (12) exiting the reactor comprises HCl, unreactedHCFO-1233xf, unreacted HF, HFO-1234yf, HFC-245cb. This reaction is sentdirectly to the first reactor without being subjected to any separation.

1. Process for preparing 2,3,3,3-tetrafluoropropene, comprising thefollowing steps: (a) catalytic reaction of 1,1,1,2,3-pentachloropropaneand/or 1,1,2,2,3-pentachloropropane with HF into a reaction mixturecomprising HCl, 2-chloro-3,3,3-trifluoropropene,2,3,3,3-tetrafluoropropene, unreacted HF and optionally1,1,1,2,2-pentafluoropropane; (b) separating the reaction mixture into afirst stream comprising HCl and 2,3,3,3-tetrafluoropropene and a secondstream comprising HF, 2-chloro-3,3,3-trifluoropropene and optionally1,1,1,2,2-pentafluoropropane; (c) catalytic reaction of the secondstream into a reaction mixture comprising 2,3,3,3-tetrafluoropropene,HCl, unreacted 2-chloro-3,3,3-trifluoropropene and HF and optionally1,1,1,2,2-pentafluoropropane; (d) feeding the reaction mixture of step(c) directly to step (a).
 2. Process according to claim 1 characterisedin that step (a) and step (c) are carried out in the gas phase. 3.Process according to claim 1 or 2 characterised in that the catalyst instep (a) and/or step (c) is a chromium based catalyst.
 4. Processaccording to any claims 1 to 3 characterised in that the catalyst is amixed catalyst.
 5. Process according to any claims 1 to 4 characteristedin that the catalyst is a supported catalyst.
 6. Process according toany claims 1 to 5 characterised in that step (a) and/or step (c) iscarried out in the presence of oxygen or chlorine.
 7. Process accordingto any claims 1 to 6 characterised in that step (a) and/or step (c) iscarried out at a temperature of 100 to 500° c, preferably from 200 to450° C.
 8. Process according to any claims 1 to 7 characterised in thatstep (a) and/or step (c) is carried out at a molar ratio of HF:Orgainicsfrom 4:1 to 100:1, preferably 5:1 to 50:1.
 9. Process according to anyclaims 6 to 8 characterised in that the molar ratio of oxygen:Organicsin step (a) and/or step (c) is 0.005 to 2,preferably 0.01 to 1.5. 10.Process according to any claims 1 to 9 characterised in that step (b)can be performed at a temperature of −90 to 150° C. and a pressure of0.1 to 50 bar abs.